High-pressure discharge lamp



48 PERCENT ECADM/UM AM4LGAM v E. B. NOEL nununo' r'ill- HIGH-PRESSUREDISCHARGE LAMP Filed July 8, 1946 MERCURY FIG. 1

April 19, 1949.

BY W dum PLUS ' AMALGAM INVENTOR: EDWARD B. NOE

52 PE ENTCA M/U 52 PERCENT ZINC HIS ATTORNEY 4 FIG 5| WAVELENGTH //vANGSTROM u/wrs 4a PERCENT Z/NC AMALGAM Patented Apr. 19, 1949HIGH-PRESSURE DISCHARGE LAMP Edward B. Noel, Cleveland Heights, Ohio,assignor to General Electric Company, a corporation of New YorkApplication July 8, 1946, Serial No. 681,824

7 Claims.

My invention relates. to electric discharge devices, and moreparticularly to electric discharge lamps of the high pressure type suchas high pressure capillary lamps.

Heretofore, where it has been desired to modify or supplement theradiation produced by an electric discharge through mercury by theaddition of metals such as zinc or cadmium or both, much difllculty hasbeen encountered due to the tendency of the amalgams to solidify therebyinterfering with and hindering the initiation and maintenance of the arcdischarge. In some types of prior art lamps employing amalgams, such ascapillary lamps, upon solidification and formation into globules, theamalgam tended to form and roll into positions away from the electrodes,in which situations starting of the lamps was difficult. Furthermore,the prior art attempts to modify the mercury arc spectrum by the use ofamalgams in place of mercury alone have left much to be desired from thestandpoint of approximating a continuous spectrum where it is desired toproduce a concentrated high intensity light source suitable for use inconnection with picture projection such as in colored motion pictureprojection systems, and the like, wherein a well balanced spectrum isdesired or required.

It is an object of my invention to provide a new and improved electricdischarge device.

It is another object of my invention to provide a new and improved highpressure electric discharge lamp.

It is a further object of my invention to provide a new and improvedhigh pressure electric discharge lamp of the capillary type employing anionizable medium comprising mercury, zinc and cadmium in optimumproportions to produce an improved spectrum.

In accordance with my invention, I provide a new and improved electricdischarge lamp of the high-pressure, high-intensity compact source type,wherein mercury, zinc and cadmium are used as an ionizable medium. Bythe use of optimum percentages of zinc and cadmium, I have obviated theprior art difficulties previously encountered in initiating andmaintaining an arc discharge in amalgams. In addition, I have found thatthe spectrum of the radiation produced nicely approximates or approachesa continuous spectrum, and contains a marked line of radiation withinthe green region of the spectrum as well as substantial radiation in thered region, without incurring an inordinate reduction in efficiency,which has heretofore been considered a serious disadvantage in the useof amalgams.

More particularly, I have found in the development of my invention, thatI can use greater amounts of both zinc and cadmium, than would normallybe expected on the basis of prior art investigations, withoutencountering difliculties in starting and maintaining an arc dischargein the amalgam. As an example, I have found that where mercury, zinc andcadmium are employed as an ionizable medium, I obtain highlysatisfactory arc starting and maintenance conditions where theindividual percentages by weight of the zinc and cadmium with referenceto the total amalgam, do not exceed 11.1 per cent.

In operation of electric discharge lamps employing the above describedamalgam, highly satisfactory results are obtained when the operatingpressure of the lamp is at or above '75 atmospheres, and preferably inthe neighborhood of atmospheres. Under such conditions, and in view ofthe physical structure incident to capillary lamp design, it is seenthat the interior wall loading of my lamp is greatlyin excess of thatpresent in the prior art devices using amalgams. For example, in onetype of lamp built in accordance with my invention, the interior wallloading of the lamp is approximately 4000 watts per square inch. In viewof this fact, I may use cooling means for the lamp in order to dissipatethe incident heat and maintain the wall temperature within a suitablerange.

A still further feature of my invention is the greatly improved spectrumproduced by the use of an amalgam containing zinc and cadmium within theabove stated range. I have found that by the Joint use of zinc andcadmium, the spectrum of visible radiation contains substantialimprovements not present when either Zinc or cadmium is used alone in anamalgam. More specifically, by using both zinc and cadmium in amountswithin the above mentioned range, I have observed in tests conducted onlamps built in accordance with my invention, that there is a marked lineof radiation within the green region, i. e., within the vicinity of the5000 Angstrom unit line and particularly at and above this line, whichis not present when either zinc or cadmium is used alone in an amalgam.Moreover, there is a substantial increase in radiation within the redregion of the spectrum over that present where either zinc or cadmium isused alone in an amalgam.

For a better understanding of my invention reference may be had to thefollowing description taken in connection with the accompanying drawingand its scope will be pointed out in the 3 appended claims. Fig. 1illustrates one type of high pressure lamp construction to which myinvention may be applied. Figs. 2-5 inclusive represent spectra datapredicated on high pressure lamps which data serve to explain theimprovements in spectra obtained by using particular amalgams; andFig. 5is a spectrum of a high pressure lamp constructed in accordance with myinvention showing the increased radiation within the green and redregions of the spectrum.

In Fig. 1, I have illustrated one type of electric discharge lamp inwhich my invention may be used, together with supporting and coolingstructure therefor. The electric discharge lamp I may be 01. the generaltype disclosed and claimed in U. S. Patent No. 2,094,694, grantedOctober 5, 1937, upon an application of Cornelius 301 et 81., and whichis assigned to the assignee of this application. A pair of electrodesare constituted by the inner extremities of suitable high temperatureresisting wires or conductors, such as tungsten conductors 2 and 3, andsealed into the ends of an elongated tubular envelope 4 which isconstructed of a high temperature resisting and transparentmaterial suchas highly refractory glass, quartz or the like. The ends 01' each of theelectrodes project short distances from the amalgam, describedhereinafter, and which is preferably positioned about the electrodes.

Supporting and coolin structure for the lamp assembly may include a pairof end members or plates 6 and I, the former of which is constructed ofinsulating material such as Textolite and the latter of which may be ofmetal such as brass to serve as one of the electrical connections to thelamp assembly. The plates 6 and 1 are held in position by retainingbolts 8 and 9 which are insulated from the metal plate I by ceramicbushings l and II. Rubber gaskets (not shown) are inserted between theends of a glass tube i2 to provide a water-tight enclosure and sealabout the lamp 1 and external electrode supporting structure to bedescribed presently.

A water intake tube 13 of metal is mounted on and extends into and isseated in plate 6, and communicates with the interior of tube i2. Aspring biased socket I4 is mounted in the intake tube [3 and extendsinto the glass tube i2 to accommodate and engage a metallic cylindricalterminal i of the lamp, which terminal is electrically connected to theconductor 2 and is cemented to the associated end tubulation of thelamp. The other end of lamp I is supported in the position shown bymeans of a slotted metal sleeve socket l6 which serves as a stationarycontact adapted to receive lamp terminal I! which is connected toconductor 3 and constitutes an I ing and cooling structure for the lampi, the velocity tube construction disclosed and claimed in U. S. PatentNo. 2,295,046, granted September 8, 1942, on my application, and whichis assigned to the assignee of this application.

Electrical connections to the assembly may be made to the lamp throughplate 1 and the exposed portion of the intake tube iii, the latter ofwhich may be electrically insulated by a rubbet water-inlet tube (notshown) to eliminate personnel hazard. If desired, an insulating cap 19and a contact assembly including an insulated bushing 20 containing abrass terminal connector 2| in contact with the tube It and socket Itmay be employed to serve as one connection to the lamp. An insulatedconductor (not shown) may be connected to connector 2 l.

I provide an ionizable medium 22 which aflords improvements in theradiation in the visible range and which approximates a continuousspectrum. In addition the ionizable medium, described immediatelyhereinafter, also radiates in the longwave ultraviolet. Heretofore,where cadmium and zinc were added to mercury in attempts to improve thespectrum of the emitted radiation, difliculties were encountered due tothe fact that the amalgamssolidifled thereby preventing the lamp orlamps from being started in a normal and satisfactory manner.

I have found that by using both zinc and cadmium in an amalgam, I canadd larger quantities of these metals than could be added separatelyheretofore, and still obtain a liquid amalgam which will permit the lampto start and operate in a normal manner. I also employ a charge of gas,preferably rare gas, at a low pressure to facilitate starting of thedischarge across the space operating the electrodes. A charge of argon,for example, at a pressure of a few millimeters to several centimetersof mercury is satisfactory for this purpose.

The amalgam may be located as illustrated in slightly enlarged spaces atthe ends of the discharge chamber, and the ends of the electrodes extendshort distances beyond the amalgam, defining therebetween the arcdischarge path.

In order to prevent devitrification of the enclosing envelope 4, whereit is constructed of quartz, I may employ as an internal coating theglaze or protective coating disclosed and claimed in my icopendingpatent application Serial No. 560,775, filed October 28, 1944, nowabandoned, and which is assigned to the assignee of this application.

I have found that by adding zinc and cadmium at the same time I can addmore of these metals to the mercury than previously could be employedseparately without encountering the above mentioned difficulties inmaintaining the atrial-- gam in liquid form. In other words, I maintainthe amalgam in liquid form even though relatively high percentages ofzinc and cadmium are employed, and still obtain satisfactory startingand operation of the high pressure lamp.

Furthermore, I have found that zinc and cadmium influence each other sothat lines appear very prominent in the spectrum, which lines areinsignificant in the spectrums of either cadmiummercury or zinc-mercuryamalgams. This fact is substantiated by reference to Figs. 24 inclusivewhich are based on observed values obtained from tests conducted onlamps containing as ioni'zable mediums mercury, cadmium-amalgam andzinc-amalgam, respectively. More particu-- larly, in connection withFig. 2 it will be observed that the mercury spectrum is deficient inradiation in the green region of the spectrum, that is within thevicinity of the 5000 Angstrom unit line. Furthermore it is to beobserved that the radiation within the red region of the spectrum, isalso relatively low. The above-mentioned deiiciencies in the green andred region are also apparent in the cadmium-amalgam spectrum shown inFig. 3. Moreover. in the zinc-amalgam spectrum shown in Fig. 4 it isalso evident that there is relatively little radiation within the greenand red regions of the spectrum.

However, as is supported by Fig. 5, the particular combination ofmercury, cadmium and zinc produces a spectrum with lines spaced atconveniently close intervals throughout the spectrum and with improvedamounts of radiation within the green region, that is at 5000 Angstromunits and above, as well as improved radiation within the red region.

I have found that the improved spectrum with augmented radiation in thegreen and red regions is obtained by employing amalgams in which theindividual percentages by weight of the zinc and cadmium do not exceed11.1 per cent of the total and wherein the lamp operates at pressures ator above 75 atmospheres. As supported by Fig. 5 it is also clear thatthe improved spectrum is obtainable by employing amalgam wherein theindividual percentages by weight of the zinc and cadmium are in theneighborhood of 5 per cent of the total amalgam. Tests conducted inaccordance with my invention indicate that the above-describedimprovements in spectrum without sacrificing starting and operatingconditions are readily obtainable by operating the lamps at pressureswithin the neighborhood of 100 atmospheres.

In one type of discharge lamp in which my invention has beenincorporated, the internal bore of the envelope 4 is approximately 1.8to 2.2 mm., and the distance between the electrodes or the dischargepath is about 25 millimeters. Such lamps have been operated at 1000watts input, producing spectra such as that shown in Fig. 5. Due to therelatively high internal wall loading, which is approximately 4000 wattsper square inch, the cooling structure as shown in Fig. 1 is entirelysatisfactory to maintain the wall temperature within a range of valueswhich afford satisfactory life for the lamps.

The above-described lamps offer important ad vantages for those fieldsof application where it is desired to use a mercury type lamp with amodified color. I have also found that some of the lines in thelong-wave ultraviolet have been enhanced so that a lamp of this typewill afford improved results in the field of blue-printing andphoto-engraving as well as in the colored motion picture field.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In a high pressure electric discharge lamp of the capillary type, thecombination comprising an envelope transparent to visible radiation andcapable of defining an arc discharge chamber at pressures at or above 75atmospheres, a pair of electrodes sealed in the ends thereof, anionizable medium comprising mercury, and zinc and cadmium in about equalpercentages which obviate the formation of solid amalgams to permitnormal starting and operation of the lamp and to produce substantialradiation within the region of the 5000 Angstrom unit line, the internalwall loading of said envelope being in the neighborhood of 4000 wattsper square inch.

2. In a high pressure electric discharge lamp of the capillary type, thecombination comprising an envelope, a pair of electrodes within saidenvelope, and an ionizable medium for supporting an arc discharge andoperable at pressures within the neighborhood of 100 atmospheres, saidmedium comprising mercury, zinc and cadmium wherein the individualpercentages by weight of 6 zinc and cadmium are approximately equal anddo not exceed 11.1 per cent of the total to obtain substantial radiationwithin the vicinity of the 5000 Angstrom unit line, the internal wallloading of said envelope being in the neighborhood of 4000 watts persquare inch.

3. In an electric discharge lamp of the capillary type for emittingradiation within the visible part of the spectrum, the combinationcomprising an envelope, a pair of electrodes sealed in said envelope,and employing an ionizable medium at an operating pressure at or above75 atmospheres, said ionizable medium comprising mercury, zinc andcadmium, the individual percentages by weight of zinc and cadmium areapproximately equal and not exceeding 11.1 per cent of the total toafford substantial radiation within the green and red regions of thespectrum, the internal wall loading of said envelope being in theneighborhood of 4000 watts per square inch.

4. In an electric discharge lamp of the capillary type, the combinationcomprising an elongated envelope pervious to visible radiation andcapable of defining an arc discharge chamber at pressures in theneighborhood of atmospheres, a pair of electrodes sealed in the endsthereof, an ionizable medium comprising mercury, zinc and cadmiumwherein the zinc and cadmium individual percentages by weight areapproximately 5 per cent of the total to produce substantial radiationwithin the green portion of the spectrum.

5. In an electric discharge lamp of the capillary type, the combinationcomprising an elongated envelope transparent to visible radiation andcapable of defining an arc discharge chamber at pressures above 75atmospheres, a pair of electrodes sealed in the ends thereof, anionizable medium comprising mercury, zinc and cadmium wherein the zincand cadmium individual percentages by weight are about equal and areapproximately 5 per cent of the total to afford substantial radiationwithin the green and red regions of the spectrum.

6. In an electric discharge lamp of the capillary type, the combinationcomprising an elongated envelope transparent to visible radiation andcapable of defining an arc discharge chamber at pressures above 75atmospheres, a pair of electrodes sealed in the ends thereof, anionizable medium comprising mercury, zinc and cadmium wherein the zincand cadmium individual percentages by weight are approximately equal anddo not exceed 11.1 per cent of the total to produce substantialradiation within the red and green regions of the spectrum, the internalwall loading of said envelope being approximately 4000 watts per squareinch.

7. A high pressure electric discharge lamp of the capillary typecomprising an envelope transparent to visible radiation, a pair ofspaced electrodes within said envelope, and an ionizable medium withinsaid envelope and consisting of a starting gas, mercury, zinc andcadmium, the individual percentages by weight of zinc and cadmium beingapproximately 5 per cent of the total amalgam, the wall loading beingsuch as to produce vaporization of the zinc and the cadmium to producesubstantial radiation within th green and red regions of the spectrum.

EDWARD B. NOEL.

(References on following page) 1 REFERENCES CITED The followingreferences are of record in the Number me of this patent: 495,632

UNITED STATES PA'I'ENTS 6 526340 Number Name Date 2,150,007 Ryde Mar.'7, 1939 2,152,987 Dorgelo et a1 Apr. 4, 1939 2,272,487 Kern et a1 Feb.10. 1942 10 FOREIGN PATENTS Country Date Great Britain Nov. 16, 1938Great Britain Sept. 28, 1940

